There are several architectures for transmitting information from one electronic device to another. A commonly used architecture is shown in FIG. 1. In this architecture the devices share a common communication structure, often called a data bus or communication bus. In this architecture, each device connected to the bus can transmit information on the bus, or receive any information transmitted on the bus. In addition the information transmitted on the bus can pass undistorted through each of the devices. The section of the communication bus connecting one device to another may be termed communication bus line or link. The physical medium through which the signal is transported can be an electrical wire or optical fiber. The signal transmitted from one device to another device on the communication bus can be a change in the voltage, an optical pulse, an electrical pulse with an underlying RF (radio frequency) modulation or similar implementations. Examples of such buses are Mil-Std-1553, CAN bus, FlexRay and others. Since the transmitted signal passes through multiple devices, it is clear that the connection to each device should not cause any changes in the signal. In a one dimensional communication bus, every device has at most two bus links connecting it to other devices. In a two dimensional or multi-dimensional communication bus there is at least one device with three or more bus links connecting it to other devices. In particular, the devices, and the communication bus links should be impedance matched to prevent reflections of the signal. Conversely, any situation in which there is a fault in the communication bus link, the fault and bus link would not be impedance matched and the result would be a reflected signal.
The communication buses described above can host a large amount of devices. A potential problem in these buses is that a fault in the bus would prevent the passage of information from devices before and after the fault. Current techniques to identify faults or failures in the bus are too costly to support use in low cost applications which some industries such as in-car communications require. U.S. Pat. No. 7,812,617 to the same assignee, describes a method to identify the fault in a communication bus. The method is based on identifying reflections in the communication bus. The reflections are caused by the fault in one of the bus links and are referred to as ‘signal tail’. U.S. Pat. No. 7,812,617 suggest a method of identifying the location of the fault by measuring the timing of such multiple tails, and using triangulation to identify the location of a fault.
Glossary
Communication bus—as used in the current disclosure the term “communication bus” means a structure connecting between different devices or modules configured to receive and transmit signals from one or more sources of the signal to one or more devices or modules hosted by the bus.
Bus link or line—as used in the current disclosure the term “bus link or line”means a continuous electric or optical line extending through two or more devices or modules on the bus.
Data bus—as used in the current disclosure the term “data bus” means a structure connecting between different devices or modules configured to receive and transmit data from one or more sources of the signal to one or more devices or modules hosted by the bus.
Impedance matched—as used in the current disclosure the term “impedance matched” means the characteristic impedance of the bus link is matched to the characteristic impedance of the device connected to the link. Also it means that the impedance of the line is constant.
Fault in the bus—as used in the current disclosure the term “fault in the bus” means a portion of a bus line or device hosted on the bus, which is not impedance matched and causes a reflection in or of the transmitted signal.
Integrity of the bus—as used in the current disclosure the term “integrity of the bus” means that no faults are identified in the line.
Physical medium—as used in the current disclosure the term “physical medium” means the material, composition and form (e.g. copper wire, optical fiber, etc.) of the communication bus link.
Signal tail—as used in the current disclosure the term “signal tail” means the temporal function of the last part of the signal.
Signal width—as used in the current disclosure the term “signal width” means the elapsed time from a threshold level crossing of the rising part of the signal, to a threshold level crossing of the falling part of the signal.
Signal rise time—as used in the current disclosure the term “signal rise time” is the time required for the signal to raise to its ON state.
Signal fall time—as used in the current disclosure the term “signal fall time” is the time required for the signal to return to its OFF state.
Pulse start—as used in the current disclosure the term “pulse start” is the section of pulse after crossing the threshold of the rising signal.
Pulse end—as used in the current disclosure the term “pulse end” is the section of the pulse before crossing the threshold of the falling signal.
Differential bus link as used in the current disclosure “differential bus link” is a bus link composed of two electrically conductive wires where the signal is the voltage difference between the wires.
System ground as used in the current disclosure the term “system ground” is a common or global electrical element to which all other voltages in the system are referenced. Any wire electrically connected to the ground will have a voltage of zero.
Short in the bus as used in the current disclosure the term “short in the bus” is a connection of at least one of the differential bus wires to the system ground or an electrical connection between the wires of the differential bus.